I prefer the X3
I can only compare the X4 to the X3, both of which I pledged on Kickstarter. The pluses over the previous model are: larger size, RGB side light, brighter light, tactical switch, replaceable 18650 battery. The most blaring feature is the sliding switch. I hate it so much it overshadows the good points. The switch slides, sometimes, but only with a specific amount of pressure, otherwise it doesn't move at all. Having the light on the lowest setting exposes the charging port. Three stars reflects the price I'd want to pay for this light.